This invention relates to hybrid integrated circuit devices and, more specifically, to hybrid integrated circuit devices in which a resistive body made of an alloy material having a very low temperature coefficient of resistance (TCR) is connected to a surface of a substrate of the hybrid integrated circuit device by a plurality of bonding wires,.
A conventional means for detecting a current is the bridge circuit 20 shown in FIG. 3. A current I.sub.0 30 flows through a resistance R.sub.0 21 in one leg of bridge circuit 20. The remainder of this leg is made up of a resistor R.sub.3. An opposite leg is made up of a resistor R.sub.1 22. A second pair of legs is made up of resistors R.sub.2 23 and R.sub.4 24. One terminal of a reference voltage source 35, represented by a breakdown, or Zener diode, is connected to the junction of resistors R.sub.1 and R.sub.0. The other terminal of reference voltage source 35 is connected to the junction of resistors R.sub.2 and R.sub.4. A plus input of a comparator 26 is connected to the junction of resistors R.sub.1 and R.sub.2. A minus input of comparator 26 is connected to the junction of resistors R.sub.3 and R.sub.4. The voltage at the minus input of comparator 26 is influenced by the current I.sub.0 flowing through resistance R.sub.0. At values of current I.sub.0 below a predetermined trip value, the output of comparator 26 is low "L". As soon as the current I.sub.0 exceeds the predetermined trip value, the output of comparator 26 changes suddenly to a high "H".
The predetermined trip voltage, or trip current, is established by the relationships of the resistances in bridge circuit 20. If the trip current is established at a maximum current in an external circuit, the "H" and "L" condition of the output of comparator 26 may be used to control the application of power, or some other condition of the external circuit, to avoid an overcurrent condition damaging the external circuit.
Japanese Laid-open Patent Publication No. 53-97470 illustrates the use of bridge circuit 20. Bridge circuit 20 is mounted on a substrate of a hybrid integrated circuit. The resistance R.sub.0 to detect a current I.sub.0 is normally a resistive body plated mainly with nickel (Ni). Since the fusing current in Ni plating is small, only currents smaller than the fusing current can be detected. Therefore, in order to detect larger currents, a greater fusing current is necessary. This can be accomplished by increasing the area or thickness of the resistive body. However, this larger area of the resistive body reduces the substrate area available to mount the bridge circuit 20. In addition, the plating time is further prolonged. So far, it has been impossible to detect currents in the range of 40 A with a hybrid integrated circuit.
Another way to detect larger currents is to use materials which have greater fusing currents. Copper foil or silver (Ag) paste have been used to solve the problem. Since the specific resistance of copper foil and Ag paste are respectively small, 0.5 m.OMEGA. and 37 m.OMEGA. per square cm, a larger current may be supplied to such a material. However, both materials present other problems. Ag paste is prepared by mixing epoxy resin with Ag powder. This results in an Ag paste having a large thermal resistance and a small electric power volume per unit area, therefore requiring an enlarged substrate area to increase the electric power volume. Copper foil has two problems. The first problem is that the substrate may be deformed as a result of the heat generated by a large current supplied to the copper foil. The second problem is that copper cannot attain a constant and stable resistance value. This is due to the imbalanced thickness of the copper foil from the rolling process or the side etching process. In addition, when using copper foil as a resistance element, it is difficult to trim the resistance, thus making it difficult to obtain an accurate detection of current.
In addition, the TCR of the copper foil and Ag paste are very high, 3800.+-.200 ppm and 2150.+-.150 ppm, respectively. Therefore, the resulting resistances are highly variable with respect to the temperature changes of the substrate. Resistance variations make it impossible to detect the current accurately. To solve this problem, a separate circuit for correcting for temperature variation is required, thus resulting in a more complex current detecting circuit.